Chemotaxis and migration of neutrophils followed by secretion of their constituents are critical processes in the acute inflammatory process. These processes have also been implicated in several acute and chronic lung diseases. Tissue infiltration by stimulated neutrophils may be involved in the development of emphysema, interstitial lung disease, adult respiratory distress syndrome, and airways hyperreactivity. Intravascular reactivity of neutrophils is also involved in the neutropenia and mild pulmonary dysfunction occurring during hemodialysis. Chemotaxis and migration of neutrophils are induced by interaction of specific stimuli with surface membrane receptors. The receptor ligand complexes are subsequently internalized. Addition of new receptors to the membrane has been reported. These new receptors might derive from an internal pool and/or might be a result of receptor recycling. We have described two monoclonal antibodies, NCD-1 and NCD-3, which were raised against the surface antigens of human neutrophils. NCD-1, when bound to the surface of neutrophils as a bivalent molecule, blocks chemotaxis and degranulation of cells exposed to the chemoattractants N-formyl-methionyl-leucyl-phenylalaine (FMLP), complement fragment C5a and zymosan activated plasma, whereas NCD-3, as a bivalent molecule, blocks chemotaxis to FMLP and does not influence cell degranulation. The surface expression of both antigens recognized by the antibodies is doubled on FMLP stimulated neutrophils. We will examine the hypothesis that the antigen recognized by NCD-1 becomes associated with the ligand receptor complex and subsequently directs intracellular trafficking of the internalized receptor thereby regulating specific functions of stimulated neutrophils. By contrast, preliminary evidence suggests that NCD-3 recognizes a portion of the FMLP receptor (not the ligand binding site). Therefore, by examining the NCD-3 antibody in conjunction with labeled FMLP, we will increase our understanding of the receptor ligand complex. These concepts will be explored using immunochemical and immunocytochemical techniques, as well as techniques allowing for isolation and examination of the purified antigens. Data collected from examination of neutrophils from healthy donors will be compared to data collected from peripheral blood neutrophils and neutrophils collected from lavages of patients with adult respiratory distress syndrome, hyperreactivity associated with asthma, and idiopathic pulmonary fibrosis. With these approaches, we will increase our understanding of the responsiveness of the neutrophil to the surrounding environment, thus paving the way for approaches to better control of the inflammatory cell function.